Insulated gate bipolar transistors (IGBTs) are an extremely attractive semi-conductor device for power applications. They are more attractive than a power-type insulated gate field effect transistor (IGFET), which is popularly referred to as a MOSFET. An IGBT can handle both high voltages and high currents with small die size and with relatively low "on" resistance. In addition, an IGBT can be switched rapidly, making IGBTs potentially useful as switches in a three phase inverter for a high power alternating current motor application.
On the other hand, the high current density capability and low "on" resistance of the IGBT also present new challenges. The possibility of device failure is aggravated when the IGBT is handling high power. By high power, we mean current densities above about 135 amps per square centimeter of active chip area, at hundreds of volts. By high frequency switching we mean on/off frequencies above about 18 kilohertz, as for example 30 kilohertz. As might be expected, significant impedance, material and mechanical problems are encountered in handling such power at high frequencies and low resistances. This is especially true for a high power/high frequency module, in which several such IGBTs are electrically paralleled. Heretofore, the foregoing problems have been so difficult that not many high power/high frequency IGBT modules have been commercially manufactured. Those that were made thus far, have been made in relatively low volume, where each module could be individually specially crafted.
In this specification, we describe distinctive substrate subassemblies that can be used for both linear-type and circular-type high frequency/high power modules that are capable of being manufactured on a commercial production basis. By commercial production basis, we mean production volumes such as are used in the automotive industry. Moreover, in describing this invention, we describe the principles by which high quality and high performance modules can be more effectively manufactured on a commercial production basis.
We describe substrate subassemblies, and methods of manufacture, testing and assembly involving such substrate subassemblies, for high power/high switching frequency IGBT modules. Use of these substrate subassemblies and methods, permit economic manufacture of high quality, high performance and high durability power modules, of even insulated gate bipolar transistors (IGBTs), at automotive-type volumes.